In the days when trains had a driver and a fireman to load coal and it was necessary to answer a call of nature you would shit on the coal shovel and then throw it in the fire as quick as possible because of smell and hygiene. As the shovel had coal dust on it, the shit did not stick. Interestingly the same shovel could be cleaned with steam and could be used to cook bacon and eggs.

A motorcyclist in a collision. He shot off his bike like shit off a shovel.

That car is fast it goes like shit off a shovel.

An orange VW caravanette, with Subaru impreza 2L engine, went like shit off a well greased shovel.